Mn(H2O) - American Chemical Society

Unilateral Exclusion of Jahn–Teller-Inactive d5 Mn(H2O)4(C7H4NO3S)22+ Guests by Strongly Distorted Host d9 Cu(H2O)4(C7H4NO3S)22+ Lattice Pancˇe Naumov,*,†,‡,§ Ljupcˇo Pejov,§ Gligor Jovanovski,§,⊥ Trajcˇe Stafilov,§ Milena Taseska,§ and Emilija Stojanovska§

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 4 1319–1326

Frontier Research Base for Global Young Researchers, Graduate School of Engineering, Osaka UniVersity, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan, National Institute for Materials Science, ICYS, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan, Institute of Chemistry, Faculty of Science, SS. Cyril and Methodius UniVersity, P.O. Box 162, MK-1001 Skopje, Macedonia, and Macedonian Academy of Sciences and Arts, P.O. Box 428, MK-1001, Skopje, Macedonia ReceiVed NoVember 19, 2007; ReVised Manuscript ReceiVed December 16, 2007

ABSTRACT: The crystal lattice of the isomorphous tetraaquabis(saccharinate)metal(II) dihydrates was employed as a structurally flexible coordination framework capable of sustaining large internal distortions to study the competitive inclusion of Jahn–Teller (JT) distorted d9 ions, [Cu(H2O)4(sac)2]2+, and JT-inactive d5 ions, [Mn(H2O)4(sac)2]2+, in binary solid solutions under thermodynamically controlled conditions of statistical mixing (sac ) saccharinate anion, C7H4NO3S-). Probing of the metal content of the solid phase showed a two-regime inclusion profile: increasing the ratio of the distorted cation relative to the undistorted one in the solution phase of up to about 35% results in linear dependence and preferred inclusion of the former with maximum concentration of 100% in the crystal and complete exclusion of the undistorted ion above that point. A mixed crystal with highest copper ratio of 63% was obtained from solution with 25% copper, which under the P21/c crystal symmetry corresponds to sustainable integrity of the undistorted lattice by substitution of up to 2/3 of its sites. This stability limit shows that four out of the six sites around each [Mn(H2O)4(sac)2]2+ ion can be substituted by distorted [Cu(H2O)4(sac)2]2+ guests under conditions of thermodynamically controlled, statistically averaged exchange. The undistorted host is very tolerant toward inclusion of strongly distorted guests. When acting as host, the distorted ion is more discriminatory toward the undistorted guest. Along with the expectation from the JT theory, structural refinement of seven crystals, including a mixed crystal with composition of [Cu0.126Mn0.874(H2O)4(C7H4NO3S)2](H2O)2, showed that metal–ligand distances are significantly affected by the metal substitution. Inclusion of the JT-active ion results in distortion of the coordination polyhedron by increasing the bond length difference between the two metal-O(water) bonds and also causes shortening of the M-N bond. Due to the rigidness caused by π-conjugation, the overall effect on the endocyclic geometry of the organic ligand is small. The anisotropic distortions around the metal ion are faithfully reflected in the stretching force constants of the coordinated water molecules and thus in the IR spectrum of the mixed crystals.

1. Introduction Nonlinear molecules with a partially filled set of degenerate orbitals exhibit Jahn–Teller (JT) instability. The effect, which is commonly referred to as “Jahn–Teller effect”, has been employed to explain some extraordinary properties of materials containing JT entities, such as high-temperature superconductivity, colossal magnetoresistance, and creation of long-lived photoinduced excited-state spin-trapped phases.1–5 Although a plethora of studies have been devoted to JT-related phenomena, their relation to the unusual physical properties of JT-active materials continues to attract the attention of inorganic chemists and solid-state physicists. The isomorphous series of hexahydrated salts of saccharin [1,2-benzisothiazol-3(2H)-one 1,1-dioxide] with the first transition row metals and cadmium [M(H2O)4(sac)2] · 2H2O [sac ) saccharinate ligand, C7H4NO3S-; M ) V(II), Cr(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II)] spans a remarkably large range of ionic radii, cell parameters, and intraand intermolecular distances. The crystals have a monoclinic P21/c cell and are composed of octahedral [M(H2O)4(sac)2]2+ units and hydrogen bonded lattice–water molecules (Figure 1). * To whom correspondence should be addressed. Tel: +81-(0)29-851-3354. E-mail: [email protected]. † Osaka University. ‡ National Institute for Materials Science. § SS. Cyril and Methodius University. ⊥ Macedonian Academy of Sciences and Arts.

Figure 1. Molecular (A) and crystal (B) structure of the isomorphous series of general formula [M(H2O)4(sac)2] · 2H2O with the atom labeling scheme.

Being sufficiently flexible to sustain large lattice strains without collapsing, this structure has frequently served as a probe into the systematic structural trends concerning both intra- and intermolecular parameters, including bond distance-order relationships,6 structural correlations regarding the geometry of the isothiazole half of the saccharinate ligand,7,8 and vibrational spectroscopic consequences of cation substitution.9,10 Outstanding members of the series with respect to their structural properties are the V(II),11 Cr(II),12 and Cu(II)13 compounds, for which the available structural and vibrational data indicate strong JT distortions that are reflected most evidently as anomalous

10.1021/cg701139y CCC: $40.75  2008 American Chemical Society Published on Web 03/05/2008

1320 Crystal Growth & Design, Vol. 8, No. 4, 2008

metal–ligand distances. Based on the structural flexibility of the crystal lattice, we presumed formation of stable solid solutions in the binary system [CuxMn1-x(H2O)4(sac)2](H2O)2 including the strongly JT-distorted guest Cu(H2O)4(sac)22+ in the lattice of the undistorted host Mn(H2O)4(sac)22+ and vice versa. In this study, the formation of solid solutions is demonstrated, and the structural and spectroscopic consequences of metal substitution are investigated on a series of novel mixed-metal saccharinate crystals. The copper-manganese saccharinate system was selected for this purpose based on a number of reasons: (a) the unit cell consists of a single formula unit per asymmetric unit, which simplifies greatly the interpretation of the correlations between the spectroscopic and structural data; (b) the structure includes both coordinated and noncoordinated water molecules involved in hydrogen bonding ranging from weak to strong, so that the influence on the JT instability on the primary as well as on the second coordination shell can be conveniently assessed; (c) in addition to the water of hydration, the effect can be also investigated on the isothiazole and phenylene halves of the organic ligand, that is, on both proximate and distant electronically π-conjugated systems; (d) the saccharinate ligand can be used to probe the effects of the JT distortions on the electronic properties of the carbonyl group and sulfonyl groups, two chemically very important functionalities.

2. Experimental Procedures 2.1. Preparation of the Mixed Crystals. Twelve aqueous solutions were prepared with identical overall molar concentration of the salt and [Mn(H2O)4(sac)2] · 2H2O/[Cu(H2O)4(sac)2] · 2H2O molar ratios of 100/0, 99/1, 97/3, 95/5, 75/25, 65/35, 50/50, 25/75, 5/95, 3/97, 1/99, and 0/100. Crystals from all solutions were obtained under identical conditions by slow evaporation of the solvent at ambient temperature. The resulting crystals [Mn1-xCux(H2O)4(sac)2] · 2H2O (with x between 0 and 1) differ by their size and habit, ranging from small well-defined crystals in the case of large manganese content to large crystal aggregate blocks in the case of large copper content. The crystal color also depends on the cation ratio and varies between colorless and light blue. 2.2. FTIR Measurements. The 8000-400 cm-1 range of the Fourier transform infrared spectra of the studied mixed crystals was recorded with a Perkin-Elmer System 2000 FT IR interferometer at room temperature (RT) and at low temperature (∼100 K, LT). A variable-temperature cell (Graseby-Specac) using liquid nitrogen was used for the LT measurements. To obtain a good signal-to-noise ratio, 128 spectra were collected and averaged at LT, while 64 scans appeared to be sufficient at RT. 2.3. Determination of the Metal Content. Copper and manganese contents were determined by flame atomic absorption spectrometry with deuterium correction using Thermo Elemental model Solaar 2 atomic absorption spectrometer. Hollow cathode lamps were used as a source. In the case of copper, a wavelength of 324.8 nm, slit of 0.5 nm, and lamp current of 4 mA were used, while in the case of manganese, the respective parameters were 279.5 nm, 0.2 nm, and 5 mA. A gas mixture of acetylene and air was used. The standard solutions were of p.a. grade, and doubly distilled water was used for preparation of the solutions. About 10 mg of samples was used to prepare the working solutions, and stock solutions for both Cu and Mn (γ ) 1000 mg L-1, Solution Plus Inc.) were used as standards. 2.4. Uv–Vis Spectroscopy. The 300–800 nm range of the absorption spectra was recorded in reflectance mode from mixtures of powdered samples of the crystals with KBr with a Jasco V-570 spectrometer. The overall mass concentration of the sample in the matrix in all cases was about 1%. 2.5. X-ray Diffraction. Diffraction data were collected from seven crystals obtained from solutions with the following metal ratios: 100/ 0, 99/1, 97/3, 95/5, 65/35, 50/50 and 5/95, corresponding to the real ratios of 100/0, 94.7/5.3, 94.6/5.4, 87.4/12.6, 1.4/98.6, 1.7/98.3, and 1.0:99.0, respectively. The crystals of the 75/25, 25/75, 3/97 and 1/99 mixed salts were of insufficient quality for X-ray diffraction. The X-ray diffraction data on the pure host (Mn) crystal and the mixed crystals

Naumov et al. Table 1. Metal Content of the Solution Phase and in the Mixed Crystals w(Mn), %

w(Cu), %

m(Mn)/m(Cu) in solution

calcd

found

calcd

found

m(Mn)/m(Cu) in crystals

100:0 99:1 97:3 95:5 75:25 65:35 50:50 25:75 5:95 3:97 1:99 0:100

10.42 10.32 10.11 9.90 7.79 6.74 5.17 2.58 0.513 0.308 0.102 0.0

9.545 8.42 8.79 7.82 3.26 0.128 0.137 0.089 0.087 0.077 0.094 0.058

0.0 0.12 0.36 0.60 3.00 4.20 5.98 8.94 11.28 11.51 11.75 11.86

0.023 0.528 0.580 1.20 5.63 10.42 9.14 10.40 10.15 11.65 11.17 12.64

99.8:0.02 94.7:5.3 94.6:5.4 87.4:12.6 36.9:63.1 1.4:98.6 1.7:98.3 1.0:99.0 1.0:99.0 0.8:99.2 1.0:99.0 0.5:99.5

were collected at room temperature on a Bruker AXS diffractometer, equipped with CCD detector. The frames were integrated with SAINT and further processed with SADABS and XPREP as part of the SHELXTL suite of programs.14 The structures were solved using direct methods15 and refined by least-squares method on F2.16 For the pure crystal, all non-H atoms were assigned anisotropic parameters. Due to the small amount of the secondary component, all structures except for the 87.4/12.6 crystal were treated as pure metal saccharinate crystals in the refinement. Due to the close proximity of positions of the two components, in the case of the mixed crystal the non-hydrogen atoms were refined as isotropic models, and the non-H atoms were included as riding bodies. The inclusion of the second component of the disordered saccharinate ligand resulted in a decrease of the primary residual value from about 18% to 5%, thus justifying the treatment of the structure as a two-component model. Restraints were applied to treat the disorder of the organic ligand: some of the bond distances of the minor component were restrained to their expected values in the pure crystal, and all atoms (except the sulfonyl oxygen atoms) were restrained to be coplanar. The positions of the C1 atom of the two components nearly coincide with each other and were treated as a single atom. The displacement parameters of the nonprimed atoms were restrained to similar values with the respective primed atoms. Occupancies of the partially occupied atoms (87.4% and 12.6% for the major and minor component, respectively) were fixed to the values determined by atomic absorption spectrometry. Hydrogen atoms of the water molecules were placed at 0.85 Å from the respective parent non-H atoms, and their coordinates were allowed to refine. The insufficient data quality prevented separate treatment of the hydration water of the two components.

3. Results and Discussion 3.1. Formation of Solid Solutions. The metal content determined by atomic absorption spectrometry showed nonuniform inclusion of the two cations in the mixed crystals (Table 1). At any cation ratio in solution phase, inclusion of Cu(H2O)4(sac)22+ in the solid phase is favored over Mn(H2O)4(sac)22+. By increasing the molar ratio of Cu2+ cations in the solution from 0% up to about one-third (increase of the ratio Mn(H2O)4(sac)22+/Cu(H2O)4(sac)22+ from 100/0 to 65/35), mixed crystals form with linear dependence (correlation coefficient 0.997) of their composition on the cation ratio in the liquid phase, and copper concentration in the solids ranging from about 0% to 100% (Figure 2). Higher concentrations of copper result in “saturation” and crystallization of pure [Cu(H2O)4(sac)2](H2O)2. Under the thermodynamically controlled conditions of our experiment, the mixed crystal with the highest copper ratio of 63% Cu was obtained from solution with 25% Cu. The result clearly shows that the inclusion of the JT distorted guest Cu(H2O)4(sac)22+ in the lattice of the undistorted host Mn(H2O)4(sac)22+ is preferred over the inclusion of the undistorted guest in the lattice of the distorted host. The stability of the host lattice is sustainable if up to 2/3 of its sites are

Jahn–Teller Distortions in Mixed Crystals

Figure 2. Plot of the molar ratio of copper and manganese cations in the crystallization solution and in the respective mixed crystals obtained by slow evaporation.

Figure 3. Relative change of the cell parameters, a axis (blue), b axis (black), c axis (red), and cell volume (green) with the composition (mol % copper) of the crystals.

replaced by distorted guests. This limiting value corresponds to statistical replacement of four Cu(H2O)4(sac)22+ out of six sites around each Mn(H2O)4(sac)22+ ion. Crystals of X-ray diffraction quality were obtained and diffraction data were collected from seven crystals with Mn(H2O)4(sac)22+/ Cu(H2O)4(sac)22+ ratios (from the atomic absorption spectrometric analysis) of 100/0, 94.7/5.3, 94.6/5.4, 87.4/12.6, 1.4/98.6, 1.7/98.3, and 1.0/99.0. The lattice parameters exhibit significant changes with cation substitution (Figure 3). By increasing substitution of the manganese sites with copper, the monoclinic unit cell undergoes compression of about 6% along the c axis compensated by expansion of about 5% along the a axis and of ca. 1% along the unique axis b. The balanced compression along the a axis and stretching, mostly along the c axis, results in nearly constant cell volume, which may be one of the reasons for the ability of the crystal to sustain its integrity upon cation substitution. 3.2. Effect of Metal Substitution on the Molecular and Crystal Structure. The crystallographic data of the seven analyzed crystals are listed in Table 2. Although all prepared solutions afforded crystalline compounds, some were of insufficient quality for X-ray diffraction analysis, while others contained too little of the secondary component to be included in the refined models. According to the metal content results and the lattice parameters calculated from the X-ray diffraction data (Table 2), the crystalline material obtained from solutions with ratios 65/35, 50/50, and 5/95 corresponds to the pure copper saccharinate. Four mixed crystals (94.7/5.3, 94.6/5.4, 87.4/12.6, and 36.9/63.1) contained notable amounts of both Mn and Cu, but only three (94.7/5.3, 94.6/5.4, and 87.4/12.6) crystallized as well-diffracting samples and were analyzed with X-ray diffraction. The higher copper content of the 87.4/12.6 crystal (12.6%) relative to the other mixed crystals resulted in clearly discernible residual features in the difference Fourier electron density map assignable to the minor JT-active component. Therefore a crystal from that batch of composition

Crystal Growth & Design, Vol. 8, No. 4, 2008 1321

[Cu0.126Mn0.874(H2O)4(C7H4NO3S)2](H2O)2 was selected for structure refinement in the two-component model. An ORTEPstyle plot of the final refined structure is presented, together with the structure of the pure Mn host, in Figure 4. As expected from the comparison of the lattice parameters of the pure host (Mn only) and guest (Cu only) crystals (Figure 3), inclusion of the JT-active copper atoms in the host lattice causes expansion of the cell along the a-axis and contraction along the c-axis, resulting in nearly constant volume. The crystallographic b-axis is also stretched, but due to its doubled length compared with the other two axes, the relative effect is twice as small. In the molecular coordinate system, expansion along the crystallographic a-axis corresponds to expansion of the coordination octahedron in the direction between N1, O1W, and O2W, while compression along c is related to compression along the bisector of MO2WO1W′. In the crystal of the pure manganese saccharinate host, the Mn-OW and Mn-N bonds in the coordination octahedron are of similar length, Mn(1)O(1W) ) 2.1593(13) Å, Mn(1)-O(2W) ) 2.2204(14) Å, and Mn1-N1 ) 2.2844(13) Å. In the pure copper saccharinate crystal, Cu-O2W is “normal” at 2.4918(18) Å, but due to the strong action of the JT effect, the other two bonds are significantly shortened, Cu-N1 ) 2.0594(15) and Cu-O1W ) 1.9491(14) Å. The bond shortening results in distortion of the coordination octahedron. In the structure of the mixed crystal, space-averaged over the crystal volume (Figure 4), the orientations of the two ligand components are slightly twisted around the M-N1 bond, appearing as very close positions of the carbonyl C atom and different positions of all other atoms. Due to the diffuse electron density of their disordered counterparts, the water molecules in the mixed crystal were treated as single-molecule models. Accordingly, as expected from the presence of both components, their protons feature large isotropic displacement parameters, the overall effect being more pronounced in the case of the O2W molecule. Actually, the oxygen atom of O2W exhibits increased thermal ellipsoids within the coordination plane even in the host crystal. The relevant intramolecular parameters are listed in Tables 3 and 4. The metal–ligand distances are significantly affected by the metal substitution: M-O1W, M-O2W, and M-N1 change from 2.1593(13), 2.2204(14), and 2.2844(13) Å to 2.125(3), 2.246(3), and 2.252(13) Å, respectively. The JTactive Cu ion results in distortion of the coordination polyhedron by increase of the difference between the lengths of the two metal-O bonds and shortening of the M-N bond, which is consistent with the expectations based on the crystals of the pure host and guest crystals. Based on extensive structure and spectra-structure correlations, it has been concluded17–19 that the structure of the exocyclic groups (CO and SO2) of the saccharinate reflects well the changes in electron density caused by the covalency of the M-N1 bond. As expected from the mainly covalent character in both components, comparison of the geometry of the C(O)-N-S(O2) fragment in pure manganese and copper saccharinate crystals shows that the intraligand structure is not significantly affected: O1-C1 ) 1.239(2), S1-O3 ) 1.4364(13), S1-O2 ) 1.4437(13), S1-N1 ) 1.6340(13), and N1-C1 ) 1.359(2) Å in the Mn crystal, and O1-C1 ) 1.237(2), S1-O3 ) 1.4347(14), S1-O2 ) 1.4347(14), S1-N1 ) 1.6559(15), and C1-N1 ) 1.359(2) Å in the Cu crystal. In line with these observations, the geometry of the sulfonyl group and of the carbonyl group in the mixed crystal are only slightly modified (S-O ) 1.427(4) and 1.497(5) Å; C-O ) 1.239(5) Å). Although the carbonyl groups of the guest molecule are slightly

largest diff. peak and hole, e · Å-3

R indices (all data)

refinement method data/restraints/params GOF (F2) final R indices [I > 2σ(I)]

reflns collected/unique

Mn/Cu ratio (solution) relative FW temp, K wavelength, Å crystal system space group a, Å b, Å c, Å β, deg V, Å3 Z calcd density, g · cm-3 abs coefficient, mm-1 crystal size, mm3 θ range, deg limiting indices

0

100/0 527.38 295(2) 0.71073 monoclinic P21/c 7.9652(5) 16.1469(10) 7.7881(5) 99.6990(10) 987.34(11) 2 1.774 0.949 0.30 × 0.20 × 0.18 2.52–27.49 -10 e h e 10 -10 e k e 20 -10 e l e 10 6009/2242 (Rint ) 0.0178) FMLS on F2 2242/10/182 1.038 R1 ) 0.0286; wR2 ) 0.0742 R1 ) 0.0310; wR2 ) 0.0758 0.324/-0.365

0.053 99/1 527.38 293(2) 0.71073 monoclinic P21/c 7.9693(8) 16.1474(15) 7.7830(7) 99.769(2) 987.02(16) 2 1.775 0.950 0.30 × 0.26 × 0.10 2.52–27.49 -10 e h e 10 -10 e k e 20 -10 e l e 10 11243/2258 (Rint ) 0.0686) FMLS on F2 2258/6/166 1.058 R1 ) 0.0266; wR2 ) 0.0718 R1 ) 0.0266; wR2 ) 0.0718 0.325/-0.484

97/3 527.38 293(2) 0.71073 monoclinic P21/c 7.964(7) 16.135(14) 7.799(7) 99.836(15) 987.4(15) 2 1.774 0.949 0.20 × 0.16 × 0.14 2.52–27.50 -10 e h e 9 -20 e k e 20 -4 e l e 9 6079/2241 (Rint ) 0.0483) FMLS on F2 2241/6/166 1.061 R1 ) 0.0345; wR2 ) 0.0821 R1 ) 0.0429; wR2 ) 0.0857 0.525/-0.412

0.054 95/5 (528.47) 293(2) 0.71073 monoclinic P21/c 7.9777(7) 16.1327(15) 7.7742(7) 99.964(2) 985.46(15) 2 1.592 0.796 0.30 × 0.20 × 0.10 2.52–27.50 -10 e h e 10 -20 e k e 20 -10 e l e 10 10944/2254 (Rint ) 0.0642) FMLS on F2 2254/25/118 0.975 R1 ) 0.0563; wR2 ) 0.1469 R1 ) 0.0614; wR2 ) 0.1505 1.474/-1.016


0.986

mole ratio of copper(II) in the metal content (x) 50/50 535.98 293(2) 0.71073 monoclinic P21/c 8.3837(5) 16.3323(10) 7.3379(4) 101.0710(10) 986.04(10) 2 1.805 1.389 0.38 × 0.20 × 0.16 2.48–27.50 -10 e h e 10 -21 e k e 21 -9 e l e 9 11242/2254 (Rint ) 0.0677) FMLS on F2 2254/6/166 1.081 R1 ) 0.0316; wR2 ) 0.0839 R1 ) 0.0342; wR2 ) 0.0852 0.351/-0.386

0.983

Table 2. Crystallographic Data for the Pure Host Crystal [Mn(H2O)4(sac)2] · 2H2O and Six Mixed Crystals [CuxMn1-x(H2O)4(C7H4NO3S)2](H2O)2


1322 Crystal Growth & Design, Vol. 8, No. 4, 2008 Naumov et al.


Crystal Growth & Design, Vol. 8, No. 4, 2008 1323 Table 3. Selected Bond Distances (Å) and Angles (deg) in the Structure of the Pure Host Crystal [Mn(H2O)4(sac)2] · 2H2Oa Mn(1)-O(1W)#1 Mn(1)-O(1W) Mn(1)-O(2W) Mn(1)-O(2W)#1 Mn(1)-N(1) Mn(1)-N(1)#1 S(1)-O(3) S(1)-O(2) S(1)-N(1) S(1)-C(7) N(1)-C(1) O(1)-C(1) O(1W)-H(1W1) O(1W)-H(1W2) O(2W)-H(2W1) O(2W)-H(2W2) O(3W)-H(3W1) O(3W)-H(3W2) O(1W)#1-Mn(1)-O(1W) O(1W)#1-Mn(1)-O(2W) O(1W)-Mn(1)-O(2W) O(1W)#1-Mn(1)-O(2W)#1 O(1W)-Mn(1)-O(2W)#1 O(2W)-Mn(1)-O(2W)#1 O(1W)#1-Mn(1)-N(1) O(1W)-Mn(1)-N(1) O(2W)-Mn(1)-N(1) O(2W)#1-Mn(1)-N(1) O(1W)#1-Mn(1)-N(1)#1 O(1W)-Mn(1)-N(1)#1 O(2W)-Mn(1)-N(1)#1 O(2W)#1-Mn(1)-N(1)#1 N(1)-Mn(1)-N(1)#1 O(3)-S(1)-O(2) O(3)-S(1)-N(1) O(2)-S(1)-N(1) O(3)-S(1)-C(7) O(2)-S(1)-C(7) N(1)-S(1)-C(7) Mn(1)-O(1W)-H(1W1) Mn(1)-O(1W)-H(1W2) H(1W1)-O(1W)-H(1W2) Mn(1)-O(2W)-H(2W1) Mn(1)-O(2W)-H(2W2) H(2W1)-O(2W)-H(2W2) H(3W1)-O(3W)-H(3W2) C(1)-N(1)-S(1) C(1)-N(1)-Mn(1) S(1)-N(1)-Mn(1)

Figure 4. ORTEP-style plots (50% probability level) of the crystal structures of the pure host crystal [Mn(H2O)4(sac)2] · 2H2O (top) and of the mixed crystal [Cu0.126Mn0.874(H2O)4(C7H4NO3S)2](H2O)2 (bottom).

stretched (1.268(18) Å) as a result of the change of the covalent nature of the metal–ligand coordination bond, compared with the effect on the metal–ligand bonds, the overall effect on the endocyclic geometry of the saccharinate ligand is much smaller. The UV–vis spectra of the mixed crystals with Mn/Cu ratios of 0.8/99.2, 1.0/99.0, 1.4/98.6, and 1.7/98.3 are deposited as Supporting Information (Figure S1). The pure manganese complex does not have an absorption band in the visible region. The blue color of the copper-containing samples is due to the broad d-d transition band with a maximum in the 730–770 nm region. Increase of the concentration of manganese of 1% in the copper(II) saccharinate crystals results in shift of the absorption maximum of several tens of nanometers, decreased band intensity, and shift of the UV absorption edge. These observations represent a joint result of the decreased strain of the ligand field around the Jahn–Teller-distorted copper(II) ion, which affects the energy difference of the electronic d-levels, and decreased population of the light-absorbing species. 3.3. The Inherent Jahn–Teller Instability and Vibronic Interactions. To provide a more profound insight into the structural and especially spectroscopic properties of the title mixed crystals, certain specific aspects related to vibronic interactions in the constituent species must be taken into account. Actually, complexes of high-spin ionic species such as Cr2+ (d4) and Cu2+ (d9) are typical examples of the validity of the Jahn–Teller theorem in practice. This is due to the odd number of eg electrons, which in an idealized octahedral environment would give rise to E electronic state. According to Jahn and Teller,20 as a result of the breakdown of the Born–Oppenheimer (BO) approximation, there will be a nuclear motion leading to removal of the degeneracy of the electronic states, the overall effect of which will be the lowering of the energy of the system. Geometrically, a distortion of the ideal octahedron occurs. Accounting for the symmetry of the electronic state (E), the

a

2.1593(13) 2.1593(13) 2.2204(14) 2.2204(14) 2.2844(13) 2.2844(13) 1.4364(13) 1.4437(13) 1.6340(13) 1.7498(16) 1.359(2) 1.239(2) 0.848(10) 0.845(10) 0.844(10) 0.842(10) 0.841(10) 0.844(10) 180.0 90.63(6) 89.37(6) 89.37(6) 90.63(6) 180.0 86.75(5) 93.25(5) 93.26(5) 86.74(5) 93.25(5) 86.75(5) 86.74(5) 93.26(5) 180.0 116.11(8) 110.85(8) 109.63(7) 111.13(8) 110.54(8) 96.92(7) 117.7(17) 101.6(18) 107(2) 131(2) 117.5(17) 112(3) 108(3) 111.10(11) 129.22(11) 119.56(7)

Symmetry code: (#1) -x + 1, -y + 1, -z +1.

coupled nuclear mode through which the removal of degeneracy will occur must be of e symmetry. Such systems with coupled degenerate states are usually named as E X e or Jahn–Teller (JT) or vibronic systems (due to the vibrational-electronic coupling, which is in the essence of the effect). In secondquantization formalism, the E X e coupling Hamiltonian is usually written in the form hˆEXe )

∑ ω (aˆ

R)(

0

+ ˆR + Ra

∑

1 + + gω0 (aˆ-R + aˆ+ ˆ -R cˆR R )c 2 R)(

)

(1)

where the generation/annihilation operators âR and cˆR correspond to the phonon and electron degenerate states, correspondingly. When the environment of the JT central ion is not ideally octahedral (e.g., MY6), that is, when one deals with, for example, complexes of the type MY4Y2′, the point symmetry is lower and degenerate representations do not occur. However, these systems are structurally very similar to the totally substituted “parent” compounds, where degenerate electronic states are possible at the undistorted geometry, and one intuitively expects


Naumov et al.

Table 4. Selected Bond Distances (Å) and Angles (deg) in the Structure of the Mixed Crystal [Cu0.126Mn0.874(H2O)4(C7H4NO3S)2](H2O)2 (M ) Mn or Cu)a M(1)-O(1W) M(1)-O(1W)#1 M(1)-N(1)#1 M(1)-N(1) M(1)-O(2W) M(1)-O(2W)#1 M(1)-N(1′)#1 M(1)-N(1′) M(1)-H(2W2) O(1W)-H(1W2) O(1W)-H(1W1) O(2W)-H(2W1) O(2W)-H(2W2) C(1)-O(1) C(1)-O(1′) C(1)-N(1′) C(1)-N(1) S(1)-O(2) S(1)-O(3) S(1)-N(1) S(1)-C(7) N(1′)-S(1′) O(2′)-S(1′) S(1′)-O(3′) S(1′)-C(7′) O(3W)-H(3W2) O(3W)-H(3W1) O(1W)-M(1)-O(1W)#1 O(1W)-M(1)-N(1)#1 O(1W)#1-M(1)-N(1)#1 O(1W)-M(1)-N(1) O(1W)#1-M(1)-N(1) N(1)#1-M(1)-N(1) O(1W)-M(1)-O(2W) O(1W)#1-M(1)-O(2W) N(1)-M(1)-O(2W) O(1W)-M(1)-O(2W)#1 O(1W)#1-M(1)-O(2W)#1 N(1)#1-M(1)-O(2W)#1 N(1)-M(1)-O(2W)#1 O(2W)-M(1)-O(2W)#1 O(1W)-M(1)-N(1′)#1 O(1W)#1-M(1)-N(1′)#1 N(1)#1-M(1)-N(1′)#1 N(1)-M(1)-N(1′)#1 O(2W)-M(1)-N(1′)#1 O(2W)#1-M(1)-N(1′)#1 O(1W)-M(1)-N(1′) O(1W)#1-M(1)-N(1′) N(1)#1-M(1)-N(1′) N(1)-M(1)-N(1′) O(2W)-M(1)-N(1′) a

2.125(3) 2.125(3) 2.252(13) 2.252(13) 2.246(3) 2.246(3) 2.28(9) 2.28(9) 2.92(6) 0.852(10) 0.853(10) 0.849(10) 0.851(10) 1.239(5) 1.268(18) 1.36(9) 1.365(13) 1.427(4) 1.497(5) 1.632(7) 1.763(5) 1.66(4) 1.485(18) 1.12(2) 1.714(17) 0.848(10) 0.851(10) 180.0 87.1(2) 92.9(2) 92.9(2) 87.1(2) 180.0(5) 89.15(11) 86.90(17) 93.10(17) 90.85(11) 89.15(11) 93.10(17) 86.90(17) 180.0 87.9(16) 92.1(16) 2.2(7) 177.8(7) 84.8(5) 95.2(5) 92.1(16) 87.9(16) 177.8(7) 2.2(7) 95.2(5)

O(2W)#1-M(1)-N(1′) N(1′)#1-M(1)-N(1′) O(1W)-M(1)-H(2W2) O(1W)#1-M(1)-H(2W2) N(1)#1-M(1)-H(2W2) N(1)-M(1)-H(2W2) O(2W)-M(1)-H(2W2) O(2W)#1-M(1)-H(2W2) N(1′)#1-M(1)-H(2W2) N(1′)-M(1)-H(2W2) M(1)-O(1W)-H(1W2) M(1)-O(1W)-H(1W1) H(1W2)-O(1W)-H(1W1) M(1)-O(2W)-H(2W1) M(1)-O(2W)-H(2W2) H(2W1)-O(2W)-H(2W2) O(1)-C(1)-O(1′) O(1)-C(1)-N(1′) O(1′)-C(1)-N(1′) O(1)-C(1)-N(1) O(1′)-C(1)-N(1) N(1′)-C(1)-N(1) O(1)-C(1)-C(2) O(1′)-C(1)-C(2) N(1′)-C(1)-C(2) N(1)-C(1)-C(2) O(1)-C(1)-C(2′) O(1′)-C(1)-C(2′) N(1′)-C(1)-C(2′) N(1)-C(1)-C(2′) C(2)-C(1)-C(2′) O(2)-S(1)-O(3) O(2)-S(1)-N(1) O(3)-S(1)-N(1) O(2)-S(1)-C(7) O(3)-S(1)-C(7) N(1)-S(1)-C(7) C(6)-C(7)-C(2) C(6)-C(7)-S(1) C(2)-C(7)-S(1) C(1)-N(1)-S(1) C(1)-N(1)-M(1) S(1)-N(1)-M(1) C(1)-N(1′)-S(1′) C(1)-N(1′)-M(1) S(1′)-N(1′)-M(1) O(3′)-S(1′)-O(2′) O(3′)-S(1′)-N(1′) O(2′)-S(1′)-N(1′) O(3′)-S(1′)-C(7′) O(2′)-S(1′)-C(7′) N(1′)-S(1′)-C(7′)

84.8(5) 180(4) 91(2) 89(2) 98.6(19) 81.4(19) 11.7(19) 168.3(19) 96.5(19) 83.5(19) 106(4) 123(4) 105(5) 119(7) 136(8) 103(9) 15.6(9) 124(2) 126(2) 122.9(5) 123.6(9) 3.9(11) 123.9(4) 121.0(9) 112(2) 113.2(5) 125.0(10) 120.6(13) 111(3) 112.0(11) 5.1(6) 119.1(2) 110.8(3) 107.7(3) 111.3(3) 108.5(3) 97.3(5) 124.4(4) 129.0(4) 106.6(4) 110.8(8) 129.5(5) 119.6(7) 113(5) 128(3) 119(5) 96.5(16) 121(3) 111.4(16) 123.6(16) 109.2(11) 95(4)

Symmetry code: (#1) -x + 1, -y + 1, -z + 1.

that effects reminiscent of the JT effect should appear in these cases, too. In cases when the first-order JT theorem does not apply (due to the lack of actual degeneracy) but the states are nearly degenerate, higher-order variants of the JT theorem are in fact applicable. These often allow for rationalization of the structural results. Just as an illustrative example, a perturbation theoretic expression for the energy of the ground electronic states reads

[

ˆ q|0〉q + 1 〈0|H ˆ qq|0〉 - 2 E0 ) 〈0|H 2

∑ n

]

ˆ q|n〉|2 |〈0|H q2 ∆E0n

(2)

ˆ q and H ˆ qq are In eq 2, q is the distortion coordinate, whereas H the first and second derivatives of the electronic Hamiltonian with respect to q. While the first term on the right-hand side of eq 2, containing q as a multiplier is the true or first-order JT contribution (nonzero only in the case of degenerate electronic states), the second term, containing q2, is responsible for the

second-order or pseudo-JT contribution. It is exactly this term that leads to a stabilization of the system upon distortion provided that there exists a low-lying state n (i.e., the value of ∆E0n is very small) having the “correct” symmetry so that 〈0|q|n〉 has a nonzero value. It is exactly this second-order (or pseudo-) JT contribution that governs the structural characteristics of the [Cu(H2O)4(sac)2] · 2H2O compound (a d9 system), as discussed in our previous studies.9,10,21,22 We have demonstrated that the structural changes of the coordination sphere around the central Cu2+ ion mostly influence the hydrogen-bonding network in this member of a series of isomorphous [M(H2O)4(sac)2] · 2H2O compounds. Due to the structural differences between this compound and the other members of the isomorphous series, certain spectroscopic manifestations of the second-order JT effect were observed and discussed in our previous papers.9,10,21,22 Similarly to the case of [Cu(H2O)4(sac)2] · 2H2O, also the


Figure 5. The O-H stretching region in the LT FTIR spectra of the protiated analogues of [Cu(H2O)4(sac)2] · 2H2O (upper curve) and [Mn(H2O)4(sac)2] · 2H2O (lower curve).

Figure 6. The O-H stretching region in the LT FTIR spectra of the protiated analogues of several [Mn1-xCux(H2O)4(sac)2] · 2H2O mixed crystals, where x is 0 (a), 0.35 (b), 0.50 (c), and 1 (d).

corresponding chromium compound [Cr(H2O)4(sac)2] · 2H2O contains a JT d4 ion in a nonideal octahedral environment. X-ray crystallographic studies of [Cr(H2O)4(sac)2] · 2H2O12 inevitably showed the manifestation of the second-order JT effect in this solid-state system. The coordination sphere around the central Cr2+ ion is characterized by a centrosymmetric arrangement of two nitrogen atoms of saccharinate ligands and four oxygen atoms from coordinated water molecules. As a direct consequence of the breakdown of the BO approximation to the second-order in a perturbation-theoretic sense, this arrangement manifests deviations from the regular pattern found in the other members of the series, similar to the case of the copper analogue: one M-O and the M-N bond are significantly shorter, while the other M-O bond is much longer. Such distortions in the case of the latter compound are two times smaller than the corresponding geometrical changes in the copper analogue. Due to

Crystal Growth & Design, Vol. 8, No. 4, 2008 1325

the relative flexibility of the hydrogen-bonding network in the crystals, the distortions within the coordination sphere of the central ion cause significant changes in the proton donor-proton acceptor distances. As mentioned above, the compounds of the type [M(H2O)4(sac)2] · 2H2O form an isomorphous series. Since mixed crystals containing various metal ions may be relatively easily obtained, this series of isomorphous compounds is actually very suitable for studying the cooperative vibronic effects, which appear when a Jahn–Teller active ion is present as a substitutent (forming a substituent-type solid solution) in a non-Jahn–Teller matrix. According to the previous discussion, in the present case we actually deal with cooperative pseudo-Jahn–Teller effect. The coupling between JT centers involves elastic flexibility of the host lattice, so that in a sense, matrix isolation of JT ions in a non-JT matrix may be used as a probe to test the matrix elastic properties. Accounting for the relatively complex hydrogenbonding network in the studied compounds and the mentioned differences in such network between JT-active and JT-inactive compounds, we expect that the cooperative pseudo-JT effect will mostly affect the hydrogen-bonding interaction in the host matrix. Aside from the approaches involving crystal structure determination, perhaps the easiest and the most straightforward method for probing the hydrogen-bonding network is vibrational spectroscopy, which could certainly shed some light at least on the range of hydrogen bond strength in the studied compounds. As a test system, the Cu-doped [Mn(H2O)4(sac)2] · 2H2O, was chosen, and a series of mixed crystals of the form [Mn1-xCux(H2O)4(sac)2] · 2H2O where x ranges from 0 to 1 were studied. 3.4. Vibrational Spectroscopy of the O-H Stretching Modes. In Figure 5, the O-H stretching region in the LT FTIR spectra of the protiated analogues of [Mn(H2O)4(sac)2] · 2H2O and [Cu(H2O)4(sac)2] · 2H2O are presented. The highest and lowest frequency bands in the case of the copper compound appear at about 3560 and 2980 cm-1 respectively. The corresponding numbers in the case of the manganese compound are 3480 and 3230 cm-1, respectively. These spectroscopic data clearly indicate that the hydrogen-bonding network in the case of the copper compound involves a much wider range of hydrogen bond strengths. In Figure 6, the O-H stretching region in the LT FTIR spectra of several [Mn1-xCux(H2O)4(sac)2] · 2H2O mixed crystals with varying x are shown (for protiated compounds). Comparison with the corresponding spectral region in the LT FTIR spectra of the pure copper compound invariably shows that the hydrogen bonding network with wide extension of hydrogen bond strengths characteristic for the case of the JT copper compound is achieved in the manganese host matrix even at values of x of 0.35. This observation represents clear manifestation of the cooperative JT effect in the O-H stretching vibrational spectra of solid hydrates. To the best of our knowledge, this is the first reported evidence of the phenomenon. The spectroscopic manifestation of the effect is so remarkable that all other possible reasons for rearrangement of the hydrogenbonding network (e.g., variations of the lattice constants due to the inclusion of the guest cation with different ionic radius, etc.) may be ruled out. This is a very good example showing the structural flexibility of a non-JT host crystal lattice and its ability to accommodate to the pseudo-JT deformations of guest JT ionic centers through rearrangement of the hydrogen-bonding network. The result can be relevant for application in the design of new crystals with exotic properties within the frame of the crystal engineering.


Acknowledgment. We thank Prof. S. W. Ng (University of Malaya) for the useful discussions on the crystallography, Dr. T. Fujita (National Institute for Materials Science) for recording the UV–vis spectra, and Dr. Xiang Gao Meng from the Central China Normal University for the collection of the X-ray data. Supporting Information Available: Plot of the UV-visible spectra. This material is available free of charge via the Internet at http:// pubs.acs.org.

References (1) Kaplan, M. D.; Vekhter, B. G. CooperatiVe Phenomena in Jahn-Teller Crystals; Plenum Press: New York, 1995. (2) Bersuker, I. B. The Jahn-Teller Effect and Vibronic Interactions in Modern Chemistry; Plenum Press: New York, 1984. (3) Falvello, L. R. J. Chem. Soc., Dalton Trans. 1997, 4463. (4) Fil, D. V.; Tokar, O. I.; Shelankov, A. L.; Weber, W. Phys. ReV. 1992, B45, 5633. (5) Jin, S.; Tiefel, T. H.; McCormack, M.; Fastnacht, R. A.; Ramesh, R.; Chen, L. H. Science 1994, 264, 413. (6) Naumov, P.; Jovanovski, G. J. Coord. Chem. 2001, 54, 63. (7) Naumov, P.; Jovanovski, G. Curr. Org. Chem. 2001, 5, 1059. (8) Naumov, P.; Jovanovski, G. Struct. Chem. 2000, 11, 19. (9) Pejov, Lj.; Jovanovski, G.; Grupcˇe, O.; Sˇoptrajanov, B. J. Mol. Struct. 1997, 410–411, 365.

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Mn(H2O) - American Chemical Society

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